There was a graded association with average sleep duration: participants with less than 7 hours of sleep were 2.94 times…more likely to develop a cold than those with 8 hours or more of sleep. The association with sleep efficiency was also graded: participants with less than 92% efficiency were 5.50 times …more likely to develop a cold than those with 98% or more efficiency. These relationships could not be explained by differences in prechallenge virus-specific antibody titers, demographics, season of the year, body mass, socioeconomic status, psychological variables, or health practices. The percentage of days feeling rested was not associated with colds.

Even if there’s a big confound that they haven’t accounted for, this is a large effect. It also goes along with our intuitions and common sense. There are plenty other correlations between less sleep and illness out there, but respiratory illness is a great proximate dampener on productivity for many of us. Also, ScienceDaily.

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Which is a good reason to be careful. There’s no way based on this to eliminate the possibility of a third variable messing up both the sleep and the immune system. It would have been nice if they’d also bothered to measure simple, obvious stuff like cortisol levels and blood sugar. Cortisol is immunosuppresive and raises blood sugar (which also kneecaps your immune system), and also is somewhat of a stimulant, so elevated cortisol could do it — and lots of things can cause that.

I know I personally get sick when I’m overstressed… which also invariably means I sleep less (and less soundly) and quite likely don’t eat as well, etc..

Unfortunately, sleep efficiency in this study is self-reported (which seems pretty subjective), and they do mention that they accounted for “psychological variables”, though I’m not sure what that means.

Which is a good reason to be careful. There’s no way based on this to eliminate the possibility of a third variable messing up both the sleep and the immune system.

what do you think is the probability that the 8-hour-optimum is a structural constraint or development outcome, as opposed to the limit on the margins of fitness (or perhaps in the EEA?). IOW, it seems that reduced need for sleep would be a major fitness increment in most pre-modern environments.

Well, if sleep is for undoing the accumulated damage of the day then selection for longer lifespans should also be selection for more sleep, all else equal. Also it’s not obvious that it’d be a good thing for an ape to be running around at night — at some point the odds of getting yourself into trouble start outweighing whatever you might spend that time doing.

According toLights Out: Sleep, Sugar, and Survival “sleeping at least nine and a half hours in total darkness in the fall and winter and switching to a diet low in carbohydrates and high in protein, vegetables, and healthy fats. would improve health. They think staying up late and eating a high carb diet in the summer is perfectly natural and healthy. One thing that sounds reasonable is that cheap artificial light brought about change and that it is only recently people have begun to sleep far less than they recommend, ( 9.5 hours in the winter).

Learning new things, at least in the case of spatial memory, quite literally keeps your brain young by ensuring a better survival rate for new brain cells in the hippocampus. However, not getting enough sleep eliminates the potential benefit of new learning on the hippocampus by suppressing neurogenesis. “Mild, chronic sleep restriction may have long-term deleterious effects on neural functioning,” according to the paper.
On the other hand, that sleep-deprived rats did better on a task requiring use of visual and odor cues compared to their better rested counterparts “implies that some kinds of cognitive function are resistant to sleep loss,” Hairston said. “This may be significant in human learning as well, and implies that it may be possible to optimize the way information is presented to rested versus fatigued individuals to take advantage of the specific neural substrates that are unaffected by sleep loss,” the researchers concluded.

Elsewhere Saplonsky (whose ‘Why Zebras Don’t Get Ulcers’ spawned a thousand science titles) says that a task like saying the months of the year backwards can be more easily leant by a sleep deprived person because they can’t access the memory of the way they have previously learnt to do it.

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